1. Field of the Invention
The invention relates to a honing tool with a diamond-plated surface for removing workpiece stock material.
2. Background Art
It is known practice in precision machining of a workpiece bore to use a diamond-plated tool that rotates and reciprocates within the bore. A honing tool can be used for removing stock as the honing tool rotates and reciprocates in the bore. Multiple tools of varying diameter are used during successive steps in the honing process. Another tool of known design comprises a cylindrical sleeve with a longitudinal opening that receives a metallic honing tool element, the radially outward edge of the element having an abrasive surface that removes stock from the interior of the bore. The innermost edge of the element is provided with a wedge surface that engages a companion wedge surface on the end of an actuator rod that can be adjusted axially with respect to the body of the honing tool. In this way, the effective operating diameter of the abrasive surface can be changed without changing tools during a honing operation. The amount of the stock removed depends upon the longitudinal positioning of the rod actuator relative to the tool.
Such honing tools have a relatively low tool life, and they are relatively costly to refurbish. In the case of high-volume manufacturing operations, tool refurbishing costs are enhanced because of the associated honing machine down time.
It is an objective of the invention to provide a precision honing tool for machining bores in a steel workpiece wherein the bore quality that can be achieved is not affected by the quality of the workpiece bore prior to machining and wherein the overall boring tool piece cost and the refurbishing cost are reduced.
A typical example of a workpiece that can be machined using the improved honing tool of the invention is a cylinder body for a diesel fuel injector for diesel engines. The cylinder body receives a plunger that is driven by a camshaft for the engine. In the case of a four-stroke cycle diesel engine, the injection stroke of the plunger will occur during each engine cycle, one stroke occurring for two revolutions of the engine camshaft.
The honing tool comprises a diamond-plated sleeve that can be expanded with a tapered mandrel extending through a central opening of the sleeve. Expansion may occur during rotation and oscillation of the tool in the workpiece bore to achieve a specific stock removal. The honing process does not require multiple steps as in prior art honing processes wherein tools of different sizes are used in successive steps during the honing process.
The sleeve is provided with a longitudinal slot that permits the diameter of the tool to expand as a tapered mandrel is adjusted relative to the sleeve, either by pulling or pushing the mandrel. The surface of the sleeve is nickel-plated with diamond granules in a spiral pattern, the grit size of the granules being chosen for a particular machining function depending upon the structure of the part, the material compensation, the coolant quantity and the tool cutting rate that are chosen. Stock can be removed to achieve bore diameter changes of one micron or less. Concentricity of the centerline of the bore can be maintained at a value of 1.15 micrometers or less, and roundness can be controlled to values within a range of zero to 1.15 micrometers.
The surface of the workpiece can be deposited in a spiral pattern wherein spaces adjacent diamond-plated portions of the surface accommodate coolant flow as the coolant flushes away the workpiece material during the honing operation.
The honing tool assembly of the invention has a tapered central opening in the sleeve. A mandrel rod with a tapered external surface engages the tapered wall of the sleeve opening throughout the length of the opening.
The sleeve and the diamond granule plating have a longitudinal slot along the length of the sleeve to permit the effective sleeve diameter to expand as a longitudinal pulling or pushing force is applied to the mandrel.